Car lacks acceleration

[747DRVR]

Hello. I've had 4173 for 3 years now. She has a stage 2 DMCH crate engine (Automatic) with about a 1000 miles on the engine. About 6 months ago I started having a complete lack of acceleration. When you step on it the revs build very slowly but eventually has no problem getting to 80 on the expressway. I'm talking 0-60 in about 20 seconds. Also when I step on it, the AC switches off until I let off on the accelerator. I have replaced the fuel pump and fuel filter but still the same. When it gets up to temperature it also sometimes idles a little rough. Any ideas?

[Jonathan]

If that's transmission related, you can check a couple different things:

1.) condition of transmission fluid filter. It is up inside the pan, so you'll need to drop the pan and replace the fluid to get to it. They plug over time and are meant to be replaced. Replacements were unavailable for a long time until forum member Michael took the initiative to get new ones made. You can buy them now through most vendors. If the filter is plugged, or partially plugged, it will rob your car of power yet the RPM's will still rise. Almost like you're momentarily in neutral.

2.) It could be just a typical case of bad shift computer wiring or internals. Did yours get rebuilt with modern electronics as part of that stage 2 upgrade? The inside of that shift computer governor box can fail from soldered joints loosening to capacitors blowing. You can also see them fail by having the wiring getting burnt because it fell down on top of the exhaust crossover pipe. You can inspect that part from underneath without taking anything out or off the car. Seeing what is inside the governor and removing completely from the car will force you to drain the ATF and drop the pan, as one of the computer harness connections goes inside the pan area.

[747DRVR]

I'm fairly certain its not the transmission. The tranny has been completely updated and seems to be functioning normally. I did change the fluid just in case a few months ago but there's definitely no slipage

[Bitsyncmaster]

I assume your still running K-jet. Did the problem happen suddenly or gradually? Did you do any work on the engine before it happened. Lack of power is usaly caused by retarded spark so make sure your getting the proper spark advance.

[747DRVR]

All of a sudden. First time driving it after about a month and no acceleration. I know that it could be a whole bunch of possibilities but I thought the AC cutting out might give someone some ideas

[David T]

Make sure you are shifting through all (3) of the gears. Possible you are only getting 3rd and that would hurt acceleration a lot. Make sure the frequency valve is buzzing. If it is not, the engine will run lean and have less power. Finally check vacuum and mechanical advance. If they aren't working you won't get all of the power.

[Ron]

Make sure you are shifting through all (3) of the gears. Possible you are only getting 3rd and that would hurt acceleration a lot. Make sure the frequency valve is buzzing. If it is not, the engine will run lean and have less power. Finally check vacuum and mechanical advance. If they aren't working you won't get all of the power.
+1

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Assuming the AC fan keeps running, a vacuum leak could cause the AC flap actuators to open/close when they shouldn't ...fits all of the symptoms.

[DMCMW Dave]

Make sure you are shifting through all (3) of the gears. Possible you are only getting 3rd and that would hurt acceleration a lot. Make sure the frequency valve is buzzing. If it is not, the engine will run lean and have less power. Finally check vacuum and mechanical advance. If they aren't working you won't get all of the power.

If that's the issue you'll also smoke the trans in short order. Be 100% sure it's shifting all 3 gears.

[Rich]

This suggestion isn't to rule out the tranny, only a simple thing to check on the engine.

It's based on 1 of the 9 possible causes of insufficient power output in Sec. C4 of the Tech. Info. Manual: "Sensor plate or control piston binding"

Remove the air filter box, then with engine off press on the air metering plate to see if it moves down smoothly. There should be the usual slight resistance from the fuel system rest pressure but it should move smoothly all the way down.

Then start the engine. In neutral open the throttle by hand to various positions/speeds while checking the corresponding metering plate movement. See if it binds or sticks when it opens or closes.

[Lenny]

I can't help it, I'm sorry.

Of course it doesn't have any acceleration, it's a DeLorean. :neener: